Electrocoating is a well known process for painting electrically charged articles by immersion in a bath of paint having an electrical charge of opposite polarity to that of the article. In this painting process up to 90%, or more, of the paint adheres to the workpiece. Also, paint coatings applied by the electrocoating process have very uniform film properties, and the thickness of the paint film is accurately controllable. Further, there are virtually no runs, sags, or tears in the paint film.
However, for a number of reasons, the electrocoating process has not heretofore been used to paint assembled engines even though that process is especially effective for completely coating a workpiece having sharp edges, points, and hidden or otherwise inaccessible outer surfaces. First, there are surfaces on an assembled engine, such as exhaust manifolds and turbocharger housings, that become very hot during engine operation. If these surfaces are coated with paint, the paint will burn off during operation, producing smoke and undesirable fumes. To avoid paint burnoff it is necessary to carefully mask the surfaces that are subsequently subjected to high operating temperatures prior to the painting operation or, alternatively, strip the surfaces after painting. Both of these operations are labor intensive and difficult to control.
Submersion of the workpiece in a fluid paint bath, an integral step in the electrocute process, makes the requirements for effective masking or subsequent stripping more difficult. Furthermore, paint applied by the electrocoat process has excellent penetrating ability and can readily flow past gaskets, seals, bearings and temporary covers over openings on the engine. This, of course, is very undesirable and can seriously damage the engine.
The present invention is directed to overcoming the problems set forth above. It is desirable to have an effective, economical process for painting an assembled engine. It is also desirable to have such a process wherein preselected portions of the assembled engine are not coated with paint in the course of carrying out the paint process, and further, that paint not enter into the internal cavities and passageways of the engine.